1. Field
The present disclosure relates generally to structures and, in particular, to structures carrying loads. Still more particularly, the present disclosure relates to a method and apparatus for carrying loads while allowing controlled displacement of the structures carrying the loads.
2. Background
With mechanical systems, different objects may be connected to each other. For example, a bridge may have towers, parts of a deck, suspension cables, and other components that are connected to each other. In some cases, the connection between objects may allow for movement, expansion, or contraction of the objects. The point of connection of two or more objects is a joint. In some cases, joints connecting two objects together may be multi-directional joints that allow movement in more than one direction.
When objects are connected to each other, dampers may be used. A damper is a physical structure connected to the objects. When a load is carried through the damper, the damper allows a controlled amount of deflection in at least one direction which reduces any force applied in that direction. In other words, a damper may arrest movement in certain directions but allow deflection and reduced loads in other directions. This process constrains relative motion between the objects in response to applied loads and forces while reducing the forces carried through the system in the directions that are able to deflect.
A damper, used with a load bearing joint, may constrain the relative motion between objects to only a few degrees of freedom. For example, a hydraulic damper, such as an automotive shock absorber, may be used to allow one-dimensional movement of a point along a line. In another example, a cylindrical elastomeric bearing may accommodate rotation about a fixed axis.
A damper may limit motion to certain degrees of freedom using a design that reduces deflection to certain directions. For example, an elastomeric bearing is comprised of layers of a deformable elastomer material and layers of a rigid material. As used herein, “rigid” material is material that does not have deflection. The rigid layers may be placed between elastomeric layers such that the rigid layers slide with resistance relative to each other but the separation or compression of the rigid layers is prevented by the stacking of the elastomeric material in thin layers between the rigid layers.
Different types of dampers are used in different situations, depending on the desired degrees of freedom of the objects and the types of loads to be applied to the objects. For example, an elastomeric bearing may be used between two parts of a deck in a bridge such that these parts may expand or contract in response to changes in temperature. As another example, an elastomeric bearing may be used in a rotor assembly for a helicopter to absorb energy from dynamic loads and vibrations from rotor blades.
The elastomeric bearing used in one situation may not function as well as desired in another situation. For example, the loads and force directions that are encountered by an elastomeric bearing used in a bridge may be very different from the loads and force directions encountered by an elastomeric bearing used in a rotor assembly for a helicopter. As a result, the desired geometry, quantity, and thickness of layers within an elastomeric bearing for one application may differ from the desired geometry, quantity, and thickness of layers for other applications.
Thus, as new applications using elastomeric bearings are implemented, new bearing designs are developed to provide a level of resistance that reduces the amount of deflection to a level desired for the new application. Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.